This invention relates to a transverse sealer of a bag maker-packaging machine of a so-called form-fill-seal type (herein referred to simply as "a bag maker") and also to a bag maker provided with such a transverse sealer.
A bag maker of the vertical pillow-type as disclosed, for example, in U.S. Pat. No. 5,237,798 issued Aug. 24, 1993, is adapted to seal together the mutually overlapping vertical edge parts of a cylindrically formed bag-forming flexible material (herein referred to as "a film"), to then seal the film pieces transversely over a narrow seal area which is to serve as the boundary between the top edge of one bag and the bottom edge of the adjoining bag to be produced and to cut the film at the center of this seal area to separate the mutually adjacent bags. When a bag maker of this type is used to package articles such as potato chips that break easily, powder-like small pieces tend to be produced copiously as they are dropped into the bags for packaging. Since such small pieces drop more slowly than the articles intended to be packaged, these small pieces are likely to get caught between the film pieces when they are transversely sealed. This affects adversely not only the appearance of the produced bags but also the air-tightness of the seals.
In view of the above, Japanese Utility Model Publication Jikkai 6-20209 disclosed a new transverse sealer provided with a pair of shutters which are placed above a pair of seal jaws and moved towards each other to thereby squeeze the cylindrically formed film immediately before the transverse sealing is effected, thereby preventing slow-falling small pieces of the articles from flowing into the area where transverse sealing takes place.
If such shutters are provided, however, care must still be taken such that the sealing operation should not be started too soon after the shutters are closed so as to prevent those small pieces which have just passed between the closing shutters from becoming caught between the seal jaws. In other words, it was difficult with a prior art transverse sealer to completely prevent powder-like small pieces from getting caught in the seal area.